Asynchronous non-constant-pitch spiral scroll-type fluid displacement machine

ABSTRACT

A scroll-type spiral fluid displacement machine having at least one pair of interfitting scroll elements. The scroll vanes of the scroll elements are constructed upon a base line spiral defined by the equation: 
         L=K   0 φ K1   e   −φ/     K2      
     where L is the distance from the spiral&#39;s origin to any point on the spiral curve, φ is the angular displacement of the spiral, K 0  is a constant greater than 1, K 1 , is a constant greater than 1, and K 2  is a constant greater than 10.

BACKGROUND OF THE INVENTION

1. Field of the Invention

This application relates generally to a spiral scroll-type fluid displacement machine and more particularly to an asynchronous non-constant pitch spiral scroll-type fluid displacement machine.

2. Description of the Related Art

Generally, a conventional spiral scroll-type fluid displacement machine is formed with a pair of scroll elements (i.e., an orbiting scroll element and a fixed scroll element) each having spiral vanes that are fitted together in a certain predetermined way to intake fluid such as air or water through an intake port. The interfitting spiral vanes create one or more fluid pockets and trap the fluid inside the pocket(s) by moving the orbiting scroll element in a predetermined manner. The fluid pocket moves toward an outlet port while maintaining pressure in the pocket by continuously moving the orbiting scroll element within the interfitted fixed scroll element. The pressurized fluid is discharged though an outlet port.

U.S. Pat. No. 801,182 (Creux) describes a conventional spiral scroll-type machine. A typical spiral scroll-type machine includes a pair of scroll elements where one scroll element is termed a fixed scroll and the other one is termed an orbiting scroll. Either the fixed or orbiting scroll comprises a spiral vane or a curled up wrap connected to an end plate in such a manner that the spiral vane is perpendicular to the planar surface of the end plate. The projecting spiral vanes or wraps of the fixed and orbiting scrolls interfit to form a plurality of line contacts between them, and thus at least one pair of fluid pockets is formed. The fixed scroll is stationary and does not move. The orbiting scroll does not rotate by revolving around its center. Rather the movement of the orbiting scroll is an orbiting motion. That is, the non-rotating orbiting scroll is moved in an orbit (generally circular in shape) formed around the center of the fixed scroll. With such orbiting motion, the line contacts between the spiral vanes of the fixed and orbiting scrolls move along the curved surfaces of spiral wraps, thereby creating fluid pockets and possibly changing the volume of (and thus the pressure in) the fluid pockets. The volume can be increased or decreased depending on the orbiting direction of the orbiting scroll, or the geometry of the spiral vane structure. Therefore, a spiral scroll type machine can compress or expand fluids for pumping action.

FIGS. 10A-10D show simplified cross-sectional views of interfitted spiral vanes of the fixed and orbiting scroll elements in a spiral scroll-type fluid displacement machine for generally illustrating the concept of the moving pair of spiral vanes moving fluid. Referring to FIG. 10A, a fluid is sucked into one of the outer openings of the interfitted spiral vanes. Only a single intake of fluid into a fluid pocket is shown for ease of illustration and understanding. As the orbiting scroll progresses along its orbital path, the fluid inlet is closed to create a fluid pocket as shown in FIG. 10B. FIG. 10C shows a complete revolution of the orbiting scroll from FIG. 10A, showing the progression of the fluid pocket toward the center of the interfitted spiral vanes. FIG. 10D shows another complete revolution of the orbiting scroll showing the progression of the fluid pocket to the center of the interfitted spiral vanes where the fluid is discharged.

In the past decade, the rapid development of the computer and the availability of high-precision CNC machines propelled a marvelous progress in this field. This type of fluid displacement machine demonstrates the following advantages:

1. High efficiency—mainly because the process of suction-compression-discharge occurs continuously and the expansion of remaining fluid into suction pocket does not exist, thereby offering a higher volume efficiency. 2. Torque varies in a relatively small range during a full rotation. Vibration is kept at the low level, as is the noise. 3. The structure is simple and compact.

The scroll-type compressor has gained increasing popularity and taken more and more market share, which used to be occupied by other types of compressors (such as the reciprocating-type compressor and rotary-type compressor, among others), especially for small-size compressors ranging in power from 0.5 to 15 kilowatts. Scroll-type fluid displacement machines are being widely used in some industries such as for air-conditioning and medical equipment. In order to meet the requirements for broader industry applications, it is desired to further optimize the design of these types of machines.

Although this design concept of scroll-type fluid displacement machines appeared as early as the beginning of twentieth century, its development was hindered due the difficulty to optimize its design and the requirement for high precision machining. A lot of effort is now being invested to improve the performance and reliability of scroll-type fluid displacement machines. Some are focusing on developing dual scroll compressors to enlarge capacity and achieve higher energy efficiency (as in U.S. Pat. Nos. 5,258,046 and 5,556,269). Some are emphasizing the axial and/or radial compliant mechanism (as in U.S. Pat. Nos. 4,846,639, 6,461,131, and 6,695,600). Some are focusing on a coating treatment on the spiral surface in order to prevent seizure or friction and provide good lubrication between scroll wraps. Some are trying to provide a better rotation preventive device (as in U.S. Pat. No. 6,752,606). Designing scroll vanes to improve the performance of compressor is one of various key areas. Some are focusing on the central portion of spiral surface (as in U.S. Pat. No. 5,513,967). Some are stressing on finding an appropriate scroll curve to increase the volume ratio (as in U.S. Pat. No. 5,458,471), or minimize the machine size (as in U.S. Pat. No. 5,318,424), or for special requirements (as in U.S. Pat. No. 5,547,353).

However, the conventional scroll-type fluid displacement machines have problems in that the fluid pressure distribution and the fluid pressure variation during operation are not optimized such that the conventional scroll-type fluid displacement machines have the shortcomings less-than-optimal efficiency, and relatively high noise and vibration, all of which contributes to decreased durability of the machines.

SUMMARY OF THE INVENTION

With the aid of sophisticated computer-based real-time measurement systems and advanced computer fluid dynamics analysis, it was found that fluid pressure distribution and variation during the operation of scroll-type fluid displacement machines is key to the design of a new fluid displacement machine structure, and to choose an appropriate curve for scroll wraps. The present fluid displacement machine overcomes the general shortcomings of current machines and manifest inherent advantages such as high efficiency, low noise, low vibration and enhanced durability. With such consideration and using an optimization technique, the present invention uses a single, continuous curve as the base line for constructing scroll vanes.

The scroll vanes of the present invention are constructed based upon a base line spiral defined by the equation:

L=K ₀φ^(K1) e ^(−φ/) ^(K2)

Wherein L is the distance from the origin to any point on the spiral curve, φ is the angular displacement of the spiral, K_(o) is a constant greater than 1, K₁ is a constant greater than 1, and K₂ is a constant greater than 10.

The fluid displacement machine according to a preferred embodiment of the present invention comprises two pairs of scroll elements, where each element is made up of a fixed scroll and an orbiting scroll. These two pairs of scroll elements are separate and mounted in a back-to-back manner. The scroll wraps of the two orbiting scrolls are symmetric with respect to the central axis of a driving shaft. So are the scroll vanes of two fixed scrolls. Two pairs of scrolls are offset by a phase difference of 180 degrees. These two orbiting scrolls share the same orbiting circle.

The scroll elements can be mounted on two separate crankshafts, of which the eccentric parts are positioned opposite radially. The two crankshafts are then linked with a rigid coupling such that the rotation force can be transmitted to the second crankshaft through the first one. The fluid displacement machine has two inlets and two outlets. The inflowing fluid will be divided and may be compressed or expanded through either pair of scrolls simultaneously. The discharged fluid from each outlet is then merged together to export.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a cross-sectional view of scroll-type fluid displacement machine in accordance with a preferred embodiment of the present invention.

FIG. 2 is an exploded perspective view showing two orbiting scrolls, two fixed scrolls, two crankshafts and one rigid coupling in the arrangement shown in FIG. 1.

FIG. 3 is a side view of the assembly of two crankshafts and one rigid coupling in accordance with a preferred embodiment of the present invention.

FIG. 4 is a diagram showing the relative position of eccentric parts of the two crankshafts in accordance with a preferred embodiment of the present invention.

FIG. 5 is a diagram showing the relative position of spiral wraps of two orbiting scrolls machine in accordance with an embodiment of the present invention.

FIG. 6 is a diagram showing an example of a spiral curve which defines the shapes of spiral wraps of the scrolls in accordance with the present invention.

FIG. 7 is a cross-sectional view of spiral wrap of an orbiting scroll used in a single-scroll compressor in accordance with a preferred embodiment of the present invention.

FIG. 8 is a cross-sectional view of spiral wraps for an orbiting scroll used in a dual-scroll compressor in accordance with a preferred embodiment of the present invention.

FIG. 9 is a cross-sectional showing the mating of an orbiting scroll with a fixed scroll which are used in a dual-scroll compressor in accordance with an embodiment of the present invention.

FIGS. 10A-10D depict cross-sectional views of mating spiral wraps showing the progression of a fluid pocket as the orbiting scroll is rotated along its orbiting path.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Referring to FIG. 1, the first fixed scroll 1 has its spiral wrap that interfits the spiral wrap of the first orbiting scroll 2. The concentric part of crankshaft 4 passes through the center hole of fixed scroll 1 and is supported by bearing 5 while the eccentric part of crankshaft 4 goes through the center hole of orbiting scroll 2 and is supported by bearing 3. The second fixed scroll 8 has its spiral wrap that interfits the spiral wrap of the first orbiting scroll 9. The concentric part of crankshaft 10 passes through the center hole of fixed scroll 8 and is supported by bearing 5 while the eccentric part of crankshaft 10 goes through the center hole of orbiting scroll 9 and is supported by bearing 3. The rigid coupling 6 connects crankshaft 4 and crankshaft 10. The fixed scroll 1 and fixed scroll 8 are affixed to the housing 7. The rotating force is transmitted to the end of crankshaft 10 so that the crankshaft 10 drives the orbiting scroll 9 to produce relative orbiting motion. Meanwhile, the force is transmitted to crankshaft 4 through rigid coupling 6 to produce relative orbiting motion. A rotation preventive device includes part 11, 12, 13, and 14, and prevents rotational movement of the orbiting scrolls 2 and 9.

The orbital movement generating mechanism for this preferred embodiment comprises two crankshafts 4 and 10 connected by the rigid coupling 6. However, the orbital movement generating mechanism could comprise a single crankshaft or any other means for producing non-rotating relative orbital movement between the orbital and fixed scrolls. It is noted that, none of the scrolls necessarily needs to be fixed as long as relative orbital movement between mating scrolls is achieved through some means.

FIG. 2 is an exploded perspective view showing the two orbiting scrolls 2 and 9, two fixed scrolls 1 and 8, two crankshafts 4 and 10 and one rigid coupling 6.

As shown in FIG. 3, the crankshaft 4 and crankshaft 10 are connected by rigid coupling 6. The eccentric part 4 a of crankshaft 4 and the eccentric part 10 a of crankshaft 10 preferably share the same diameter and length. The eccentric distance of 4 a is preferably equal to that of 10 a.

FIG. 4 is a diagram representing the relative positioning of the crankshafts 4 and 10 described in FIG. 3. C0 represents the cross-section of the thickest concentric part of crankshaft 4. C1 represents the cross-section of the eccentric part 4 a of crankshaft 4 while C2 is the cross section of the eccentric part 10 a of crankshaft 10.

C3 represents the orbiting circle along which the center of C1 and the center of C2 travel. The orbiting scroll 2 is mounted on eccentric part 4 a and the orbiting scroll 9 is mounted on eccentric part 10 a, so these two orbiting scrolls share the same orbiting circle. When connecting crankshaft 4 and crankshaft 10, it is preferred that the centers of the eccentric parts 4 a and 10 a of both crankshafts 4 and 10 are located radially oppositely with respect to the circle C3. Such an arrangement simplifies the balancing of the machine. As shown in FIG. 4, the center of C1, O1, is located at the top of C3 while the center of C2, O2, is located at the very bottom of C3. When crankshaft 4 is rotating in a counter-clockwise direction, the circle C1 representing the eccentric part 4 a orbits along the circle C3 from the top of C3 counter-clockwise, and the circle C2 representing the eccentric part 10 a orbits along the circle C3 from the bottom of C3. During the rotation cycle, eccentric parts 4 a and 10 a always remain at radially opposite positions.

FIG. 5 depicts the relative overlapping positioning of the spiral wraps of two orbiting scrolls 2 and 9. The rotating axis of the concentric part of crankshaft 4 goes through point O. As shown in FIG. 5, orbiting scrolls 2 and 9 are symmetric around the point O. Therefore, the mass distribution of orbiting scroll 2 and that of orbiting scroll 9 would normally also be symmetric around the point O, if the orbiting scrolls are both uniformly made of the same material. The need for balance weight to balance the orbiting scroll is thus eliminated.

The scroll-type fluid displacement machine in accordance with present invention preferably comprises two inlets and two outlets. Referring back to FIG. 1, there are inlets. 1 a and 8 a, and there are outlets 1 b and 8 b. The inflowing fluid is divided and fed into the two inlets 1 a and 8 a, processed in the two pairs of scrolls, discharged through each outlet 1 b and 8 b, and merged together to export.

The non-constant-pitch spiral curve shown in FIG. 6 is used as the base line to define the spiral vanes of the orbiting scrolls. The defining equation for such a spiral curve is:

L=K ₀φ^(K1) e ^(−φ/) ^(K2)

where

L: the distance from the origin to any point on the spiral curve;

φ: the angular displacement of the spiral curve

K₀: a real number greater 1, (K₀>1)

K₁: a real number greater 1, (K₁>1)

K₂: a real number greater 10, K₂>10

The strategy to select an appropriate spiral curve is:

1. To obtain a high volume ratio. The ratio of the displacement (V_(s)) to the final compression volume (V_(e)) is required to be high enough to meet the requirement according the application of the scroll-type fluid displacement machine.

2. To use a single, continuous, smoothly changing curve to define the scroll wraps for its entire length. It is required that the change of the volume of the fluid pocket formed between two scrolls be smooth and continuous in order to increase or decrease the fluid pressure smoothly and avoid shock.

3. When the former two conditions are satisfied, it is desired to have a spiral curve, which defines a faster change of volume of the fluid pocket. In so doing, the full cycle of suction-processing-discharge is shortened. Energy efficiency can be also enhanced.

The particular curve shown in FIG. 6 is defined by the equation:

L=2φ^(1.5) e ^(−φ/100)

It is important to note that this particular curve is just a member of a family of curves that are described by the equation. In practice, the consideration of performance requirements including power, physical properties of fluid and pressure ratio, will be included in the design of the curve. All these requirements must be met with the highest priority. Then the curve will be optimized to enable the fluid displacement machine to achieve its optimum performance in terms of its fluid dynamics. The result of optimization is the best combination of three parameters: K₀, K₁ and K₂. The intended machine will be improved in the following aspects: increased operating efficiency, reduced vibration, reduced noise and increased durability.

The proposed curve can be used to construct a scroll vane for a single-scroll fluid displacement machine as well as dual-scroll fluid displacement machine. A typical method is employed to construct the scroll vanes for a single-scroll fluid displacement machine. FIG. 7 shows the constructed cross-section of an orbiting scroll 20. The scroll vane of the corresponding fixed scroll 22 is symmetric to the vane of the orbiting scroll around the origin.

The proposed curve can be also adopted in the design of dual-scroll fluid displacement machine. A typical dual-scroll fluid displacement machine has a crankshaft which goes through the fixed scroll 22 and the orbiting scroll 20. In order to allow the eccentric part of the crankshaft to pass through the central portion of orbiting scroll 20, the spiral scrolls must start from some angular offset, such as is depicted in FIGS. 8 and 9 where an angular offset of 141° in the second turn counting from the center. FIG. 8 depicts the cross-section of spiral wraps of orbiting scroll 20. The dimensions 4.35 mm, 5.79 mm, and 5.16 are shown in FIG. 8 as an example of one embodiment for one optimum case; nevertheless, it should be clearly understood that the present invention is not just limited to the dimensions shown in FIG. 8. Other optimum dimensions satisfying the equation L=K₀φ^(K1)e^(−φ/) ^(K2) besides those shown in FIG. 8 are also possible. The mating between the orbiting scroll 20 and the fixed scroll 22 is shown in FIG. 9.

It will be clear that the present invention is well adapted to attain the ends and advantages mentioned as well as those inherent therein. While various embodiments including the presently preferred one has been described for purposes of this disclosure, various changes and modifications may be made, which are well within the scope of the present invention. Numerous other changes may be made which will readily suggest themselves to those skilled in the art and which are encompassed in the spirit of the invention disclosed and as defined in the appended claims. 

1. A scroll-type fluid displacement device comprising: a first scroll and a second scroll, each scroll having an end plate from which a spiral projects transversely from the end plate; said first scroll and said second scroll being opposingly arranged to interfit said spirals; said spirals being opposingly symmetrical about a central axis; a base line for each spiral be defined by the equation: L=K ₀φ^(K1) e ^(−φ/) ^(K2) wherein L is the distance from said central axis to any point on the base line curve, φ is the angular displacement of the base line curve, K_(o) is a constant greater than 1, K₁ is a constant greater than 1, and K₂ is a constant greater than
 10. 2. The device according to claim 1 further comprising an orbital movement generating mechanism that moves at least one of the scrolls so that said first scroll moves in a non-rotating orbital path perpendicular to said central axis, relative to said second scroll.
 3. The device according to claim 1 further comprising a housing to which one of said scrolls is rigidly affixed.
 4. The device according to claim 2 wherein said orbital movement generating mechanism is a rotationally driven crankshaft.
 5. The device according to claim 1 further comprising a third scroll and a fourth scroll that are defined and interfit in the same manner as said first and second scrolls; wherein said first and third scrolls are rigidly affixed to a housing; and wherein said second and fourth scrolls are driven in a non-rotating orbital path perpendicular their respective central axes, relative to said first and third scrolls.
 6. The device according to claim 5 wherein the central axes of said second and fourth scrolls are parallel; wherein said second and fourth scrolls are driven in the same direction on their respective orbital paths and at an angular phase difference of 180 degrees.
 7. The device according to claim 5 wherein said second and fourth scrolls share a common central axis.
 8. A method of designing scroll elements for a scroll-type fluid displacement device, the steps comprising: designing a base line spiral for first and second scroll elements, the base line spiral being defined by the equation: L=K ₀φ^(K1) e ^(−φ/) ^(K2) wherein L is the distance from a central axis to any point on the base line curve, φ is the angular displacement of the base line curve, K_(o) is a constant greater than 1, K₁, is a constant greater than 1, and K₂ is a constant greater than 10; designing inner and outer spirals to define spiral walls that create fluid pockets having a desired change in volume when said first and second scroll elements are fit and orbitally rotated together in the scroll-type fluid displacement device. 